That isn't surprising.  The neck is a flexible 'soft' surface, and the choker
is a 'hard' object.  When the neck bends, the choker isn't going to expand
and contract automatically.

Easiest solution, I think, would be a little less choke.  In other
words, increase the X and Z scale on the choker until it looks good at
various non-extreme neck positions.

Alternatively you could build the choker as a conforming figure, but
that would be a LOT of work.

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